This invention relates to apparatus and methods for taking samples from multiple sources. It has particular application to an automatic sampler mechanism for use with liquid chromatrographs.
The efficiency with which the sample is used is an important factor in the construction and operation of autosampler mechanisms. There are two parameters which contribute to the efficiency. One of the parameters is the minimum amount of sample that must be in the sample tube to enable the sample to be removed for use in the liquid chromatograph. A second parameter which contributes to the efficiency is the amount of sample that must be removed from a vial containing the sample in order to be able to inject the sample into the liquid chromatograph.
A number of mechanisms have been used in the prior art for withdrawing samples from sample vials. These prior art mechanisms include syringe transport mechanisms and purge mechanisms.
In the prior art syringe transport mechanisms the syringe is physically inserted into the sample vial, a portion of the sample is drawn into the syringe, and the syringe is then removed from the sample vial and mechanically moved and connected to another sample injection mechanism.
Prior art purge mechanisms operated by purging a sample loop. Purge mechanisms used in the prior art were uncontrolled, that is, gas pressurization or suction alone was relied on to move the sample from the vial into loop; and such purge mechanisms were usually used with a complete loop fill only.
The prior art syringe transport offers the benefit of low waste level, i.e. only the amount of the sample to be injected is removed from the vial by the syringe. As a result, multi samples may be taken and rejected to waste to minimize cross contamination before one sample is injected into the chromatograph, and the syringe transport is still a relatively efficient mechanism. However, the prior syringe transport mechanisms have a number of problems, including problems of mechanical alignment and high pressure seals.
The purge mechanisms which use gas pressurization or suction to remove samples from the vial require flexible lines in order to accomodate the movement of the needle into the sample vial. This has made it necessary to remove relatively large volumes, in excess of 30 milliliters of sample in order to purge the system. Also, only fixed volumes could be injected using prior art purge mechanisms of this type.
Primary objects of the present invention include minimizing the dead volume between the sample point and the injection point, allowing for variable volume injection, minimizing mechanical alignment problems, controlling the volume removed, and providing for efficient flush and cleanout of the system.